Thermoelectric generator

ABSTRACT

A thermoelectric generator includes a plurality of thermoelectric modules that generate electrical power when subjected to a temperature differential. The generator also includes a plurality of first thermal elements to which heat is supplied by a first fluid and a plurality of second thermal elements from which heat is removed by a second fluid. The first and second thermal elements are arranged in a stack of alternating first and second thermal elements having one of the plurality of thermoelectric modules between each adjacent pair of first and second thermal elements. Each thermoelectric module is in contact on its first side with one of the first thermal elements and in contact on its second side with one of the second thermal elements such that no face of any thermal element contacts more than one of the thermoelectric modules.

This application claims priority to U.S. provisional application 61/060,377, filed Jun. 10, 2008 and titled “Combined Heat and Power and Hydrogen Generation for Whole Home or Building with Ground Heat Exchanger Using Thermoelectric Seebeck Modules”, the disclosure of which is hereby incorporated herein in its entirety for all purposes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______ (Attorney docket number 027483-000210US), titled “Integrated Energy System for Whole Home or Building”, and to U.S. patent application Ser. No. ______ (Attorney docket number 027483-000300US), titled “Automatic Configuration of Thermoelectric Generation System to Load Requirements”, both having the same inventor as the present application and filed Jun. 10, 2009. The disclosures of those two applications are hereby incorporated herein in their entirety for all purposes.

BACKGROUND OF THE INVENTION

A thermoelectric module is a device that exploits the thermoelectric effect exhibited by many materials. FIG. 1 shows a typical thermoelectric module 100. A thermoelectric module such as module 100 has the property that when current is passed through the module, for example at terminals 101, one side 102 of the module is cooled and the other side 103 is heated. Thermoelectric modules are used in this way in certain consumer devices such as water coolers and the like.

The thermoelectric effect is reversible, such that when the two sides of a thermoelectric module are held at different temperatures, the module can generate electric power. For example, in FIG. 1, rather than driving a current through terminals 101 to heat and cool module sides 102 and 103, the module sides 102 and 103 may be held in a temperature differential, and a voltage will be produced across terminals 101. The voltage produced and the amount of power available from the module depend on the temperature differential between the two sides 102 and 103, the materials used to construct the module, the absolute temperature at which the module is operated, the size of the module, and other factors. For example, a typical commercially available thermoelectric module about 34×31 millimeters may produce about 1.5 watts of power at about 2.8 volts when subjected to a temperature differential of about 100° C. While this amount of power is sufficient for certain small loads, it is small in comparison with the power requirements of a typical home. For practical power generation, it may be necessary to combine the outputs of a number of thermoelectric modules. Preferably, the modules can share the same hot and cold sources, and are electrically interconnected such that their combined power output is available for use.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, a thermoelectric generator for generating electrical power from a difference in temperature includes a plurality of thermoelectric modules. Each thermoelectric module has a first side and a second side, and each thermoelectric module generates electrical power when subjected to a temperature differential between its respective first side and second side. The thermoelectric generator also includes a plurality of first thermal elements to which heat is supplied by a first fluid, and a plurality of second thermal elements from which heat is removed by a second fluid. The first and second thermal elements are arranged in a stack of alternating first and second thermal elements having one of the plurality of thermoelectric modules between each adjacent pair of first and second thermal elements. Each thermoelectric module is in contact on its first side with one of the first thermal elements and in contact on its second side with one of the second thermal elements such that no face of any thermal element contacts more than one of the thermoelectric modules. Each of the first and second thermal elements may be a block made of a thermally conductive material, and each block may further comprises a passageway through the block through which the respective fluid flows. The thermally conductive material may be aluminum. Each block may be generally rectangular, and each passageway may traverse its respective block generally diagonally. Each passageway may include a lead-in portion at each end, each lead-in portion being generally cylindrical and of a larger dimension than the midportion of the passageway. The first and second thermal elements may be mechanically interchangeable.

In some embodiments, the thermoelectric generator further comprises a clamp that holds the stack of thermoelectric modules and first and second thermal elements in compression. In some embodiments, the thermoelectric generator comprises a first fluid inlet manifold that distributes the first fluid to the first thermal elements, and a first fluid outlet manifold that collects the first fluid from the first thermal elements. In some embodiments the thermoelectric generator further comprises a second fluid inlet manifold that distributes the second fluid to the second thermal elements, and a second fluid outlet manifold that collects the second fluid from the second thermal elements. In some embodiments, the thermoelectric generator comprises a first fluid inlet manifold that distributes the first fluid to the first thermal elements, a first fluid outlet manifold that collects the first fluid from the first thermal elements, a second fluid inlet manifold that distributes the second fluid to the second thermal elements, and a second fluid outlet manifold that collects the second fluid from the second thermal elements. The first fluid inlet manifold and the second fluid outlet manifold may be positioned adjacent each other on one side of the stack of thermoelectric modules and first and second thermal elements.

In some embodiments, the thermoelectric generator further comprises one or more flexible tubes, at least one of the tubes connecting each of the manifolds with each of its respective first or second thermal elements. At least one of the flexible tubes may be press fit into its respective manifold and thermal element. The first fluid may be water. The second fluid may be water.

In another embodiment, a method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature comprises providing a plurality of thermoelectric modules, each thermoelectric module having a first side and a second side, and each thermoelectric module generating electrical power when subjected to a temperature differential between its respective first side and second side. The method further comprises providing a plurality of first thermal elements configured to receive heat from a first fluid, and providing a plurality of second thermal elements configured to be cooled by a second fluid. The first and second thermal elements are arranged in a stack of alternating first and second thermal elements having one of the thermoelectric modules between each adjacent pair of first and second thermal elements. Each thermoelectric module is in contact on its first side with one of the first thermal elements and is in contact on its second side with one of the second thermal elements such that no face of any thermal element contacts more than one of the thermoelectric modules. In some embodiments, the method further comprises providing a first fluid inlet manifold configured to receive the first fluid and distribute it to the plurality of first thermal elements. The method may further comprise providing a second fluid inlet manifold configured to receive the second fluid and distribute it to the plurality of second thermal elements. The method may further comprise providing a first fluid outlet manifold configured to receive the first fluid from the plurality of first thermal elements and carry the first fluid away from the thermoelectric generator. The method may further comprise providing a second fluid outlet manifold configured to receive the second fluid from the plurality of second thermal elements and carry the second fluid away from the thermoelectric generator. The method may further comprise connecting each thermal element to a fluid inlet manifold and to a fluid outlet manifold. The method may further comprise clamping the stack of first thermal elements, second thermal elements, and thermoelectric modules, so that that stack is held in compression.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical thermoelectric module.

FIG. 2 shows one example arrangement for supplying a temperature differential to a single thermoelectric module.

FIG. 3 shows one possible consequence of placing two thermoelectric modules of different heights between a single hot thermal element and a single cold thermal element.

FIG. 4 illustrates a thermoelectric generator in accordance with an example embodiment of the invention.

FIG. 5 shows a schematic view of a thermoelectric generator in accordance with another embodiment.

FIG. 6 shows an oblique view of the thermoelectric generator of FIG. 5.

FIG. 7 shows an oblique view of a thermal element, in accordance with an embodiment.

FIG. 8 shows the thermal element of FIG. 7 in cross section.

FIG. 9 illustrates a thermal element in accordance with another embodiment.

FIGS. 10A and 10B illustrate a method of making connections between flexible tubes and thermal elements, in accordance with an embodiment.

FIGS. 11A-11D illustrate several ways of making manifolds, according to embodiments of the invention.

FIG. 12 illustrates a thermoelectric generator in accordance with another example embodiment.

FIG. 13 illustrates a thermoelectric generator in accordance with still another example embodiment.

FIG. 14 illustrates the use of a thermoelectric generator in a system wherein one fluid is heated using solar energy, and another fluid is cooled using an earth-coupled piping loop.

DETAILED DESCRIPTION OF THE INVENTION

Thermoelectric module 100 is but one example of a thermoelectric device usable by embodiments of the invention. Module 100 is made up of a number of thermoelectric elements 104, each of which is a length of conductive or semiconductive material with favorable thermoelectric properties. For example, the elements may be pieces of n-type and p-type semiconductor material, labeled “N” and “P” in FIG. 1. The thermoelectric elements 104 are arranged in thermoelectric couples, each thermoelectric couple including one “N” element and one “P” element. The ends of the elements in each thermoelectric couple are electrically connected at hot side 103 of module 100 by one of conductors 105, and are further thermally connected to a heat source through an optional header 106. The various thermoelectric couples are connected in series at cold side 102 of module 100, by conductors 107, and are also thermally connected to a “cold” source or header 108 at the cold side 103 of module 100. Each thermoelectric couple generates a relatively small voltage, and the voltage appearing at leads 101 is the accumulated voltage of the series-connected thermoelectric couples. While many thermoelectric modules are made using n-type and p-type semiconductor materials for the thermoelectric elements 104, it will be understood that the invention is not so limited. Many other kinds of materials known and yet to be developed exhibit the thermoelectric effect, and may be used in embodiments. Similarly, other arrangements of the elements may be envisioned.

Preferably, thermoelectric modules used in embodiments of the invention are optimized for power generation. Research has shown that the total power available is maximized when the length “L” of the thermoelectric elements is quite short—for example about 0.5 millimeters. However, the conversion efficiency of a thermoelectric module (the fraction of available thermal energy actually converted to electrical energy) increases with increasing length L. For example, a thermoelectric element with a length of 5.0 millimeters may be several times more efficient than one with a length of 0.5 millimeters. The optimum length for a particular application (providing the minimum cost per expected unit of electrical energy) will be a function of the cost of the thermoelectric modules and associated hardware, the cost of the thermal energy supplied to the thermoelectric generator, and the expected life of the thermoelectric generator. A more complete discussion of the factors involved in optimizing the performance of a thermoelectric module may be found in D. M. Rowe and Gao Min, Evaluation of thermoelectric modules for power generation, Journal of Power Sources 73 (1998) 193-198.

For maximum power output, it is advantageous to supply heat to the hot side of each thermoelectric module as efficiently as possible, and to remove heat from the cold side as efficiently as possible. FIG. 2 shows one example arrangement for a single thermoelectric module 200. In FIG. 2, thermoelectric module 200 is sandwiched between a heat source 201 and a heat sink 202. For example, heat source 201 may be a thermally conductive block through which a relatively hot fluid 203 is circulated, and heat sink 202 may be a thermally conductive block through which a relatively cold fluid 204 is circulated. Heat source 201 and heat sink 202 may be aluminum blocks through which relatively hot and cold water are circulated respectively. One of skill in the art will recognize that the terms “hot”, “cold”, “heated”, and “cooled” are used in a relative sense. Hot fluid 203 may not appear hot to normal human senses, and cold fluid 204 may not appear cold. “Hot” and “cold” mean that the hot fluid is at a higher temperature than the cold fluid, and not that a person would necessarily perceive the fluids as “hot” or “cold.” Similarly, a heat source and a heat sink may be provided by a structure other than a simple block. For the purposes of this disclosure, an element that supplies heat to or removes heat from a thermoelectric module will be referred to as a “thermal element.”

The assembly shown in FIG. 2 may also be subject to a compressive force F, for example supplied by a clamping arrangement not shown. A compressive force helps ensure that heat source 201 and heat sink 202 make good thermal contact with thermoelectric module 200, minimizing the thermal resistance at the interfaces.

If the outputs of more than one thermoelectric module are to be combined, it is preferable that the complexity of fluid and electrical connections be minimized, and that each thermoelectric module makes good thermal contact with a heat source and a heat sink. Achieving good thermal contact for all thermoelectric modules may be complicated by the variability of dimensions inherent in any manufacturing process. For example, not all thermoelectric modules may be of the same height. FIG. 3 shows one possible consequence of placing two thermoelectric modules 301, 302 of different heights between a single hot thermal element 303 and a single cold thermal element 304. (The difference in height between thermoelectric modules 301 and 302 is somewhat exaggerated in FIG. 3.) As is easily seen, it may not be possible to achieve planar contact with all of the surfaces of thermoelectric modules 301 and 302, and the heat transfer between thermoelectric modules 301 and 302 and thermal elements 303 and 304 may be compromised. Gaps such as gap 305 may be formed, ultimately resulting in poor power generation performance of the system. Increasing the compressive force F may improve contact between the system components by bending or conforming the components, but excessive forces may result in damage to the various components.

One approach to this problem is described in co-pending U.S. patent application Ser. No. 10/823,353, filed Apr. 13, 2004 and titled “Same Plane Multiple Thermoelectric Mounting System”, the disclosure of which application is hereby incorporated herein in its entirety for all purposes. That application describes an arrangement in which at least some of the thermal elements are configurable to accommodate tolerance variations in the system components, enabling the efficient coupling of multiple thermoelectric modules.

FIG. 4 illustrates a thermoelectric generator 400 in accordance with an embodiment. For the purposes of this disclosure, a “thermoelectric generator” is an arrangement of one or more thermoelectric modules and other components that generates electric power using the thermoelectric effect. Each thermoelectric module may be made up of a plurality of thermoelectric elements, arranged in thermoelectric couples.

Example thermoelectric generator 400 includes a plurality of thermoelectric modules 401. Each thermoelectric module 401 generates electrical power when subjected to a temperature differential between its two sides. Thermoelectric generator 400 also includes a plurality of first thermal elements 402 to which heat is supplied by a first fluid 403, and a plurality of second thermal elements 404, from which heat is removed by a second fluid 405. The first and second thermal elements 402 and 404 are arranged in a stack of alternating first and second thermal elements, with a thermoelectric module 401 sandwiched between each adjacent pair of a first thermal element 402 and second thermal element 404. While only four thermoelectric modules 401 are shown in Figure, with three first thermal elements 402 and two second thermal elements 404, one of skill in the art will recognize that more or fewer thermoelectric modules may be used.

Other than the first thermal elements on the ends of the stack, each first thermal element 402 is then in contact with two of thermoelectric modules 401, one at each of two opposing faces of the respective first thermal element 402. Similarly, each second thermal element 404 is in contact with two of thermoelectric modules 401, one at each of two opposing faces of the respective second thermal element 404. However, no face of any thermal element is in contact with more than one thermoelectric module 401. In this way, efficient use of the thermal elements 402, 404 is made, but manufacturing variances in the components are tolerated. Height variations in the thermoelectric modules 401 do not compromise the system performance, because each face of the thermal elements 402, 404 need only conform flatly to one side of one thermoelectric module 401. The thermoelectric modules 401 and thermal elements 402, 404 are free to conform in various translational and rotational degrees of freedom during assembly to accomplish the conformance.

Thermal elements 402, 404 may be made from a thermally conductive material, such as a metal. Aluminum is a preferred material, due to its high thermal conductivity and resistance to corrosion. Example thermal elements will be described in more detail below.

First fluid 403 is distributed to the first thermal elements 402 by a first fluid inlet manifold 406. First fluid 403 may be, for example, water that has been heated for the purpose of generating electric power from thermoelectric generator 400, waste hot water from a industrial process, or from some other source. First fluid 403 may be another kind of fluid, for example a natural or synthetic oil, or any other kind of suitable fluid. For the purposes of this disclosure, the term “fluid” is intended to be interpreted broadly, and encompasses liquids such as water, oil, or other liquids, and encompasses gasses such as air, steam, and other gasses. First fluid 403 preferably passes through a passageway in each of first thermal elements 402, exemplified by passageway 407. After passing through first thermal elements 402, first fluid 403 is collected by a first fluid outlet manifold 408 to be carried away from thermoelectric generator 400. Fluid 403 may be returned to a heating system, or simply exhausted from the system.

Similarly, second fluid 405 is distributed to second thermal elements 404 by a second fluid inlet manifold 409. Second fluid 405 is at a different temperature than first fluid 403, and may be of the same kind as first fluid 403, or may be a different kind of fluid. For example, both first and second fluids 403 and 405 may be water, or one may be water while the other is a kind of oil. Any suitable combination is possible. Preferably, second fluid 405 passes through passageways in second thermal elements 404, exemplified by passageway 410. After passing through second thermal elements 404, second fluid 405 is collected by a second fluid outlet manifold 411, to be carried away. Second fluid 405 may be recycled, or exhausted from the system.

The net result is that each of thermoelectric modules 401 is exposed to a temperature differential, by virtue of being between one of first thermal elements 402 and one of second thermal elements 404. Thermal energy flowing through each thermoelectric module 401 is converted to electrical energy, and a voltage is developed across each set of electrical leads 412. In some embodiments, leads 412 may be interconnected such that thermoelectric generator 400 produces a single voltage on a single set of leads. For example, thermoelectric modules 401 may be connected in series, so that thermoelectric generator 400 produces a voltage that is the sum of the voltages produced by the individual thermoelectric modules 401.

While a particular arrangement of components has been described above, one of skill in the art will recognize that variations are possible within the scope of the claims. For example, thermoelectric generator 400 has been described has having “hot” first thermal elements 402 and “cold” second thermal elements 404. This relationship may be reversed, so that the end thermal elements are “cold”. Similarly, thermoelectric generator 400 is shown having first fluid 403 and second fluid 405 flowing counter to each other through the thermal elements 402, 404. That is, as shown in FIG. 4, first fluid 403 flows right-to-left through first thermal elements 402, and second fluid 405 flows left-to-right through second thermal elements 404. In some embodiments, the fluids could flow in the same direction, or in parallel flow. Many other variations are possible. For example, the passageways 407, 410 in the first and second thermal elements 402, 404 may be oriented perpendicular to each other, or in some other orientation. One preferred arrangement is described in more detail below.

FIG. 5 shows a schematic view of a thermoelectric generator 500 in accordance with another embodiment. While the stacked orientation of the thermoelectric modules 401 and thermal elements 402, 404, enables good thermal contact in spite of variations in the dimensions of the various components, these variations may also affect other aspects of the assembly. For example, as shown in FIG. 5, the spacings of the passageways through thermal elements 402, 404, may vary. Two of these distances are labeled D₁ and D₂ in FIG. 5. If the thermoelectric modules 401 are not all of the same height, or if there are manufacturing variations in the thermal elements 402, 404, D₁ and D₂ may differ, and ports formed in the manifolds such as first fluid inlet manifold 406 may be misaligned with the passageways. Because the spacing is not predictable without extensive measuring and sorting of the individual components, it is preferable to accommodate these variations as well. In FIG. 5, the thermal elements 402, 404 are connected to the manifolds 406, 408, 409, 411, through flexible tubes 501. (Not all of the flexible tubes are labeled in FIG. 5). Flexible tubes 501 may be made, for example, of rubber or plastic tubing that is easily conformable to accommodate small displacements between the passageways in thermal elements 402, 404 and openings in the manifolds 406, 408, 409, 411.

FIG. 6 shows an oblique view of the thermoelectric generator of FIG. 5. Thermoelectric modules 401 are not visible in FIG. 6, other than that their electrical leads 412 are shown protruding from between adjacent pairs of first thermal elements 402 and second thermal elements 404. First fluid 403 enters first fluid inlet manifold 406, flows through some of flexible tubes 501, through first thermal elements 402, through more of flexible tubes 501 into first fluid outlet manifold 408, and out of the system. Similarly, second fluid 405 enters second fluid inlet manifold 409, flows through some of flexible tubes 501, through second thermal elements 402, though more of flexible tubes 501 into second fluid outlet manifold 411, and out of the system. For clarity of illustration, flexible tubes 501 are shown in FIG. 6 as having appreciable length, with the various manifolds being held a distance away from the thermal elements. In practice, it is preferable to make flexible tubes short, in order to reduce surface area from which usable thermal energy may be lost. In one example embodiment, manifolds 406, 408, 409, 411 are made of one inch (25.4 mm) square tubing, and only about ¼ inch (6.35 mm) of each of flexible tubes 501 is exposed between its respective manifold and thermal element.

In one arrangement, the fluids pass through their respective thermal elements generally diagonally. As is shown in FIG. 6, passageway 407 crosses the top first thermal element 402 generally from one corner to the opposite corner. This arrangement ensures that first fluid 403 imparts heat to the first thermal elements 402 near the center of the thermoelectric modules, and also provides a relatively large contact surface between the fluid 403 and each of thermal elements 402. The remaining first thermal elements 402 are preferably arranged in the same orientation. Second thermal elements 404 may be flipped, so that their internal passageways (not shown in FIG. 6) also cross the second thermal elements 404 generally diagonally, and cross the passageways of the first thermal elements 402. The first and second thermal elements 402, 404 may be mechanically the same, and the criss-cross fluid flow accomplished by simply flipping the second thermal elements 404 upside down with respect to the first thermal elements 402. More detail about the thermal elements will be given below.

FIG. 6 also illustrates a clamp that holds the stack of thermoelectric modules and first and second thermal elements in compression. In the example embodiment shown, an upper plate 601 and a lower plate 602 are tied together by rods 603, which are held in tension by screws 604. Many other clamping arrangements are possible. For example, rods 603 may be threaded rods, and a nut at each end may draw plates 601 and 602 together. In another embodiment, one or more springs may be attached between plates 601 and 602. Many other mechanisms are possible for holding the modules in compression.

FIG. 7 shows an oblique view of one of first thermal elements 402, in accordance with an embodiment. A thermoelectric module 401 (simplified in FIG. 7) is shown as it may be positioned with respect to element 402. An opening 701 is visible on one face, leading to a passageway 407 through element 402. Passageway 407 leads generally diagonally to a complementary opening on the opposite face of element 407. A section of flexible tube 501 is shown protruding from the opening in the opposite side of element 402. FIG. 8 shows first thermal element 402 in cross section, and more clearly illustrates the internal structure of element 402. Opening 701 may be a stepped hole including a lead-in portion that is of a larger diameter than the midportion of the passageway, providing a shoulder 801 against which a tube such as flexible tube 501 may abut when the tube is inserted into opening 701. Shoulder 801 can thus aid in the proper assembly of thermoelectric generator 400. Passageway 407 passes entirely through element 402, reaching a similar stepped opening 802 at the other side of element 402. Passageway 407 may be formed, for example, by drilling or boring overlapping holes from openings 701 and 802.

The generally diagonal traverse of element 402 by passageway 407 enables identical mechanical parts to be used for first thermal elements 402 and second thermal elements 404. In other words, the first and second thermal elements 402, 404 are mechanically interchangeable. First thermal elements 402 and second thermal elements 404 are simply flipped with respect to each other, so that their respective passageways cross. When thermoelectric modules 401 are positioned as shown in FIG. 7, the diagonal passageways traverse the thermal elements generally across the longest dimension of the thermoelectric modules 401.

Many other arrangements are possible. For example, the passageways through the thermal elements may be orthogonal to the sides of the thermal elements. FIG. 9 illustrates this arrangement, in a partially exploded oblique view. In FIG. 9, first thermal element 901 includes an opening 902 in face 903, leading to a passageway 904 that traverses thermal element 901 generally orthogonally to face 903. Although not illustrated in FIG. 9, opening 902 and other similar openings may be stepped openings. Passageway 904 leads to a complementary opening 905 on the opposite face of thermal element 901. A section of flexible tubing 501 is shown protruding from complementary opening 905. A second thermal element 906 may be mechanically interchangeable with first thermal element 901, but flipped or rotated so that its passageway 907 is perpendicular to passageway 904 in first thermal element 901. A thermoelectric module 401 is sandwiched between first and second thermal elements 901 and 906. These components may be part of a larger stack of alternating first and second thermal elements 901, 906 with a thermoelectric module 401 between each adjacent pair of thermal elements 901, 906. In this embodiment, manifolds would be placed one at each side of the stack of thermal elements 901, 906, rather than in pairs on two sides of the stack as was shown in FIG. 6. Two manifolds 909, 910 are shown in FIG. 9. The thermoelectric modules may be placed in alignment with the thermal elements, as thermoelectric module 401 is shown aligned with thermal element 906 in FIG. 9. Alternatively, the thermoelectric modules may be rotated with respect to the thermal elements, in the arrangements shown by phantom thermoelectric module 908 in FIG. 9. This arrangement positions the thermoelectric modules such that the passageways 904, 907 traverse the thermoelectric modules generally diagonally, if desired.

In other embodiments, the various connections between the components may be made in any number of ways. One method of connecting flexible tubes 501 to thermal elements 402, 404 was illustrated in FIG. 8. Referring again to FIG. 8, preferably openings 701 and 802 and tubing 501 are sized such that inserting a piece of tubing 501 into one of the openings results in a secure press fit. In some embodiments, the fluids passing through thermal elements 402, 404 need not be at a high pressure, so that a light press fit may suffice to prevent leakage of fluid from the connections. Similar press fits may be used to connect sections of tubing 501 to the manifolds, such as manifolds 406, 408, 409, and 411. Such press fits, with the flexible tubes 501 pressed into relatively rigid materials used for the manifolds and thermal elements, may accommodate pressure fluctuations well, as higher pressure in the flexible tubes 501 tends to improve the seal between the tubes and the receptacles into which the tubes are inserted. Preferably, flexible tubes 501 are made as short as possible, while still accommodating the tolerance variations, in order to help maximize the efficiency of thermoelectric generator 400 by minimizing heat loss from the hotter fluid to the surrounding environment, or heat gain into the colder fluid. For example, when ½ inch (12.7 mm) plastic or rubber tubing is used for flexible tubes 501, as little as ¼ inch (6.35 mm) or less of tubing may be exposed between each respective manifold and thermal element.

FIGS. 10A and 10B illustrate another method of making connections between flexible tubes 501 and the thermal elements, represented by thermal element 1001. In this embodiment, thermal element 1001 comprises a substantially rigid protruding tube 1002, over which a section of flexible tubing 501 may be clamped or otherwise fitted. For example, tube 1002 may be a metal or plastic tube that is press fit into a stepped opening in thermal element 1001, or threaded into a threaded hole in thermal element 1001. Tube 1002 may include serrations or ridges 1003 on its outer surface, for gripping and sealing to tubing 501. If tube 1002 and thermal element 1001 are both made of metal, they may be made of the same metal in order to reduce the possibility of corrosion in the system. Alternatively, tube 1002 may be made of a polymer, such as nylon, polyvinylchloride, acetal, or another suitable polymer. In FIG. 10A, tube 501 is shown poised for connection to tube 1002. In FIG. 10B, tube 501 has been assembled to tube 1002, and an optional clamp 1004 affixed to help ensure a secure and leak-free fit. Example clamp 1004 is affixed by crimping, but many other kinds of clamps are possible, including spring clamps, clamps that are tightened by use of a screw or bolt, or other kinds of clamps.

Similar kinds of connections may be used to connect flexible tubes 501 to the fluid inlet and outlet manifolds, such as manifolds 406, 408, 409, and 411. That is, tubes 501 may be pressed, threaded, or otherwise inserted into openings in the manifolds, may be fitted over tubes protruding from the manifolds, with or without clamps, or may be connected in any other suitable way. Combinations of connection types may be used. For example, the connections to the thermal elements may be of one type, while the connections to the manifolds may be of another type. Connection types may also be mixed within the connections to the thermal elements, within the connections to the manifolds, or both.

FIGS. 11A-11D illustrate several ways of making manifolds such as manifolds 406, 408, 409, 411, in accordance with embodiments of the invention. In the embodiment of FIG. 11A, a manifold 1101 includes a round tube segment 1102 that is welded or brazed into a square tube 1103. Round tube 1102 is convenient, for example, for receiving a tube or hose 1104 that in operation supplies fluid to or receives fluid from manifold 1101. Hose or tube 1104 may be compression fit, clamped, or otherwise connected to round tube 1102. Preferably, round tube 1102 and square tube 1103 are made of the same metal, so that the risk of corrosion may be reduced in the system. Square tube 1103 also includes side holes 1105 for receiving flexible tubes 501 that lead to their respective thermal elements. The number of side holes 1105 will depend on the number of thermal elements in the stack of thermal elements in the particular thermoelectric generator that manifold 1101 is part of, and on whether the manifold is for the first or second fluid. Distal end 1106 of manifold 1101 may be plugged, capped, crimped, or otherwise sealed.

FIG. 11B shows a manifold 1107 in accordance with another embodiment. In this embodiment, manifold 1107 is formed from a single piece of tubing, with a round portion 1108 and a square portion 1109. The transition 1110 between the round portion 1108 and square portion 1109 may be formed, for example, by a swaging process. Square portion 1109 may include side holes 1111, and may be sealed at its distal end 1112.

FIG. 11C shows a manifold 1113 in accordance with another embodiment. Manifold 1113 is shown as generally fabricated in the same way as manifold 1101, with a round tube 1114 welded or brazed into a square tube 1115, but manifold 1113 may be fabricated in any other suitable way as well. Manifold 1113 includes side tubes 1116 for receiving flexible tubes 501. Side tubes 1116 may be, for example, welded or brazed to square portion 1115, may be pressed or threaded into holes in square portion 1115, or may be affixed in some other suitable way. Alternatively, manifold 1113 may be molded from a polymer such as nylon, polyvinylchloride, acetal, or another suitable polymer. Round tube 1114, side tubes 1116, or both may include serrations or ridges for facilitating the secure connection of hose 1104, flexible tubes 501, or both.

FIG. 11D shows a manifold 1117 in accordance with yet another embodiment. Manifold 1117 is made from a single round tube 1118 with an open end 1119 for receiving hose 1104, and a sealed end 1120. Side holes 1121 receive flexible tubes 501 in any suitable manner as needed.

While several example manifolds have been described, it is to be understood that these are examples, and other arrangements using different combinations of features and fabrication techniques may be envisioned within the scope of the claims.

FIG. 12 illustrates a thermoelectric generator 1200 in accordance with another example embodiment. In example thermoelectric generator 1200, there are two stacks 1201, 1202 of first and second thermal elements 402, 404, and a thermoelectric element 401 between each vertically-adjacent pair of first and second thermal elements in each stack. (Thermoelectric elements 401 are visible only by their leads 412 in FIG. 12.) Horizontally-adjacent pairs of first thermal elements 402 are coupled by a tube 501, and horizontally-adjacent pairs of second thermal elements 404 are likewise coupled. Preferably, tubes 501 are quite short, to avoid radiant and other heat loss to the surrounding environment. The relative positions of first fluid inlet manifold 406 and second fluid outlet manifold 411 are interchanged, as compared with the generator shown in FIG. 6. First fluid 403 thus flows into first fluid inlet manifold 406, flows serially through first thermal elements 402, and out of first fluid outlet manifold 408. In each of the parallel paths through first thermal elements 402, fluid passes through two first thermal elements 402 in series. Second fluid 405 follows a similar path through second thermal elements 404. Passing through one set of first and second thermal elements 402, 404 may reduce the temperature differential between first and second fluids 403, 405 by only a small amount, so that passing through another set of first and second thermal elements 402, 404 may still produce useful electrical power from a thermoelectric module sandwiched between the second set.

A thermoelectric generator in the configuration of generator 1200 may be especially suitable for systems that do not recirculate the heated or cold fluids. Generator 1200 may produce more electrical energy from a single pass of fluids 403, 405 through it as compared with a generator without series-connected thermal elements, although the efficiency of generator 1200 may be slightly reduced. Whether to use series-connected thermal elements or not may be an economic decision based on many factors, such as the cost of thermoelectric modules 401, whether fluid is recycled for reheating after passing through the thermoelectric generator, and other factors. One of skill in the art will recognize that any practical number of series-connected columns of thermal elements may be used, and the columns may contain any practical number of thermoelectric elements 401, from as few as one and ranging upward. The thermoelectric modules 401 may be electrically connected in any suitable configuration, including in series, in parallel, or in a combination of serial and parallel connections.

While a thermoelectric generator such as those shown in FIGS. 6 and 12 combines the electrical outputs of several thermoelectric modules 401, this kind of generator may still produce only a few watts of usable electric power. According to statistics published by the Energy Information Administration in the United States, an average US household may use over 10,600 kilowatt-hours of electrical energy per year. This translates to an average continuous power consumption of about 1,200 watts (W) throughout the year. Even if significant conservation measures are implemented, a thermoelectric generator for household use would desirably be able to produce several hundred watts of power.

FIG. 13 shows a thermoelectric generator 1300, in accordance with another embodiment. In thermoelectric generator 1300, several generators such as those shown in FIGS. 6 and 12 are further connected. For the purpose of discussing FIG. 13, a generator such as is shown in FIGS. 6 and 12 will be referred to as a “bank”. Each bank provides a temperature differential to several thermoelectric elements 401. Thermoelectric generator 1300 further connects several banks to further increase the amount of power generated. The banks are mounted in an array on rack 1301, shown in cutaway view. The inlet and outlet tubes of the various manifolds are thus presented in an array behind rack 1301.

Fluids are provided to and received from the bank manifolds via large manifolds 1302, 1303, 1304, 1305. Large manifolds 1302-1305 may be made, for example, of 2-inch (50.8 mm) square tubing with round hose connection tubes formed, welded, or brazed on the ends. The lower ends are crimped, capped, welded shut, or otherwise sealed.

In the example of FIG. 13, large manifold 1302 supplies heated fluid to each bank's heated fluid inlet manifold, and large manifold 1303 supplies cold fluid to each bank's respective cold fluid inlet manifold. Large manifolds 1304 and 1305 receive the heated fluid and cold fluid respectively after the fluids have passed through the banks. The various fluid flows are shown only by arrows in FIG. 13. No piping or tubing is shown, so as not to obscure the interconnections. One of skill in the art will recognize that tubes, hoses, or pipes will be used to make the actual connections, and that large manifolds 1302-1305 will preferably be positioned close to the banks so as to minimize the loss of usable thermal energy. Using the rack arrangement of FIG. 13, many banks, comprising many thermoelectric modules, can be thermally connected. The leads 412 of the various thermoelectric modules can be conveniently electrically interconnected, so that the system is scalable to produce large amounts of power. (The electrical interconnections are not shown in the Figures.)

The banks of FIG. 13 are configured for “parallel” flow heat exchange, with all inlets on the lower sides of the banks, and all outlets on the upper sides of the banks. In this arrangement, all fluid flow through the thermal elements is (diagonally) upward, and entrapment of air in the thermal elements may be minimized or avoided. Air entrapped in the thermal elements can reduce the effectiveness of heat transfer between the respective fluids and thermal elements, and ultimately reduces the power available from the thermoelectric generator.

A thermoelectric generator such as thermoelectric generator 500, 1200, or 1300 may be especially suited for use when low-cost sources of hot and cold fluids are available. For example, FIG. 14 illustrates the use of thermoelectric generator 500 in a system 1400 wherein one fluid is heated using solar energy, and another fluid is cooled using an earth-coupled piping loop.

In system 1400, a solar collector 1401 concentrates incoming energy from the sun 1404 onto a tube 1403 that carries a fluid such as water or an oil. Solar collector 1401 may be driven by a motor 1402 or other actuator to follow the sun during the day, for optimum energy collection. One of skill in the art will recognize that other kinds of solar collectors may be used besides the concentrating trough type collector 1401. The fluid in tube 1403 heats a reservoir 1405. Preferably, reservoir 1405 is filled with water, which has good thermal storage characteristics and is inexpensive, although other media could be used. The fluid from reservoir 1406 may be circulated directly through tube 1403, or may be heated indirectly, such as by a heat exchanger that extracts heat from the fluid in tube 1403 and imparts it to the fluid in reservoir 1405. Preferably, the fluid in reservoir 1405 is circulated through thermoelectric generator 500, providing the “hot” side of a temperature differential from which thermoelectric generator 500 generates electric power.

While thermoelectric generator 500 is depicted in FIG. 14 as a simple block, it will be recognized that it may include the components shown in FIG. 5, including multiple thermoelectric modules, thermal elements, manifolds, and flexible tubing.

In system 1400, the cold side of the temperature differential is provided by a fluid, preferably water, that is cooled using an earth-coupled piping loop 1406. Such a loop takes advantage of the fact that at sufficient depths, the underground soil temperature stays relatively constant throughout the year. For example, in some parts of the United States, the underground temperature may be about 54-57° F. (12-14° C.). A sufficiently long earth-coupled loop will exhaust to the earth the heat gathered by the cold fluid during electricity generation in thermoelectric generator 500, cooling the fluid so that it can once again provide the cold side of the temperature differential exploited by thermoelectric generator 500. Both the hot and cold fluids and the fluid in tube 1403 may be circulated by pumps not shown in FIG. 14.

Electric power is thus generated and is available at leads 1407 of thermoelectric generator 500. Multiple thermoelectric modules within thermoelectric generator 500 may be connected in series, parallel, or in a combination of series and parallel connections to provide power having appropriate voltage, current, or other characteristics. One or more components of the system may be configurable to adjust the amount or character of the available power. For example, a matrix switch may be provided that configures the electrical interconnections of the thermoelectric modules or banks of such modules included in thermoelectric generator 500. Such configurable components, including a matrix switch, are described in co-pending U.S. patent application Ser. No. ______ titled “Automatic Configuration of Thermoelectric Generation System to Load Requirements”, previously incorporated by reference herein.

The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims. 

1 A thermoelectric generator for generating electrical power from a difference in temperature, the thermoelectric generator comprising: a plurality of thermoelectric modules, each thermoelectric module having a first side and a second side, and each thermoelectric module generating electrical power when subjected to a temperature differential between its respective first side and second side; a plurality of first thermal elements to which heat is supplied by a first fluid; a plurality of second thermal elements from which heat is removed by a second fluid; wherein the first and second thermal elements are arranged in a stack of alternating first and second thermal elements having one of the plurality of thermoelectric modules between each adjacent pair of first and second thermal elements, each thermoelectric module in contact on its first side with one of the first thermal elements and in contact on its second side with one of the second thermal elements such that no face of any thermal element contacts more than one of the thermoelectric modules.
 2. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, wherein each of the first and second thermal elements is a block made of a thermally conductive material, each block further comprising a passageway through the block through which the respective fluid flows.
 3. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 2, wherein the thermally conductive material is aluminum.
 4. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 2, wherein each block is generally rectangular, and wherein each passageway traverses its respective block generally diagonally.
 5. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 2, wherein each passageway comprises a lead-in portion at each end of the passageway, each lead-in portion being generally cylindrical and of a larger dimension than the midportion of the passageway.
 6. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, wherein the first and second thermal elements are mechanically interchangeable.
 7. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, further comprising a clamp that holds the stack of thermoelectric modules and first and second thermal elements in compression.
 8. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, further comprising: a first fluid inlet manifold that distributes the first fluid to the first thermal elements; and a first fluid outlet manifold that collects the first fluid from the first thermal elements.
 9. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, further comprising: a second fluid inlet manifold that distributes the second fluid to the second thermal elements; and a second fluid outlet manifold that collects the second fluid from the second thermal elements.
 10. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, further comprising: a first fluid inlet manifold that distributes the first fluid to the first thermal elements; a first fluid outlet manifold that collects the first fluid from the first thermal elements; a second fluid inlet manifold that distributes the second fluid to the second thermal elements; and a second fluid outlet manifold that collects the second fluid from the second thermal elements.
 11. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 10, wherein the first fluid inlet manifold and the second fluid outlet manifold are positioned adjacent each other on one side of the stack of thermoelectric modules and first and second thermal elements.
 12. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 10, further comprising one or more flexible tubes, at least one of the tubes connecting each of the manifolds with each of its respective first or second thermal elements.
 13. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 12, wherein at least one of the flexible tubes is press fit into its respective manifold and thermal element.
 14. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, wherein the first fluid is water.
 15. The thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 1, wherein the second fluid is water.
 16. A method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature, the method comprising: providing a plurality of thermoelectric modules, each thermoelectric module having a first side and a second side, and each thermoelectric module generating electrical power when subjected to a temperature differential between its respective first side and second side; providing a plurality of first thermal elements configured to receive heat from a first fluid; providing a plurality of second thermal elements configured to be cooled by a second fluid; arranging the first and second thermal elements in a stack of alternating first and second thermal elements having one of the thermoelectric modules between each adjacent pair of first and second thermal elements, each thermoelectric module in contact on its first side with one of the first thermal elements and in contact on its second side with one of the second thermal elements such that no face of any thermal element contacts more than one of the thermoelectric modules.
 17. The method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 16, the method further comprising: providing a first fluid inlet manifold configured to receive the first fluid and distribute it to the plurality of first thermal elements.
 18. The method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 16, the method further comprising: providing a second fluid inlet manifold configured to receive the second fluid and distribute it to the plurality of second thermal elements.
 19. The method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 16, the method further comprising: providing a first fluid outlet manifold configured to receive the first fluid from the plurality of first thermal elements and carry the first fluid away from the thermoelectric generator.
 20. The method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 16, the method further comprising: providing a second fluid outlet manifold configured to receive the second fluid from the plurality of second thermal elements and carry the second fluid away from the thermoelectric generator.
 21. The method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 16, the method further comprising: connecting each thermal element to a fluid inlet manifold and to a fluid outlet manifold.
 22. The method of fabricating a thermoelectric generator for generating electrical power from a difference in temperature as recited in claim 16, the method further comprising: clamping the stack of first thermal elements, second thermal elements, and thermoelectric modules, so that that stack is held in compression. 